When combustion occurs in an environment with excess oxygen, peak combustion temperatures increase which leads to the formation of unwanted emissions, such as oxides of nitrogen (NOx). One known technique for reducing unwanted emissions such as NOx involves introducing chemically inert gases into the fresh air flow stream for subsequent combustion. By thusly reducing the oxygen concentration of the resulting charge to be combusted, the fuel burns slower and peak combustion temperatures are accordingly reduced, thereby lowering the production of NOx.
In an internal combustion engine environment, such chemically inert gases are readily abundant in the form of exhaust gases, and one known method for achieving the foregoing result is through the use of a so-called Exhaust Gas Recirculation (EGR) system operable to controllably introduce (i.e., recirculate) exhaust gas from the exhaust manifold into the fresh air stream flowing to the intake manifold.
EGR operation is typically not required under all engine operating conditions, and known EGR systems accordingly include a valve, commonly referred to as an EGR valve, for controllably introducing exhaust gas to the intake manifold. Through the use of an on-board microprocessor, control of the EGR valve is typically accomplished as a function of information supplied by a number of engine operational sensors.
It is important to monitor the functionality of EGR valve control mechanisms for faults or failures that may occur during operation thereof. For example, if an EGR valve position sensor fails due to valve sticking, in-range, out-of-range or related failure conditions, it is desirable to monitor such conditions and log appropriate faults when they occur. Moreover, it is further important to distinguish failure conditions associated with an EGR position sensor from those associated with an EGR valve actuator, and to distinguish failure conditions associated with either of these mechanisms from those associated with an EGR valve actuator control system. What is therefore needed is a system for diagnosing certain fault conditions associated with an EGR valve position sensor, and for further isolating which of the one or more EGR valve position control system components are responsible for detected failure conditions.